Solar energy will satisfy an important part of future energy needs. While the need in solar energy output has grown dramatically in recent years, the total output from all solar installations worldwide still remains around 7 gigawatts, which is only a tiny fraction of the world's energy requirement. High material and manufacturing costs, low solar module efficiency, and shortage of refined silicon limit the scale of solar power development required to effectively compete with the use of coal and liquid fossil fuels.
The key issue currently faced by the solar industry is how to reduce system cost. The main-stream technologies that are being explored to improve the cost-per-kilowatt of solar power are directed to (i) improving the efficiency of solar cells that comprise solar modules, and (ii) delivering greater amounts of solar radiation onto the solar cell. In particular, these technologies include developing thin-film, polymer, and dye-sensitized photovoltaic (PV) cells to replace expensive semiconductor material based solar cells, the use of high-efficiency smaller-area photovoltaic devices, and implementation of low-cost collectors and concentrators of solar energy.
While the reduction of use of semiconductor-based solar cells is showing great promise, for example, in central power station applications, it remains disadvantageous for residential applications due to the form factor and significantly higher initial costs. Indeed, today's residential solar arrays are typically fabricated with silicon photovoltaic cells, and the silicon material constitutes the major cost of the module. Therefore techniques that can reduce the amount of silicon used in the module without reducing output power will lower the cost of the modules.
The use of devices adapted to concentrate solar radiation on a solar cell is one such technique. Various light concentrators have been disclosed in related art, for example a compound parabolic concentrator (CPC); a planar concentrator such as, for example, a holographic planar concentrator (HPC) including a planar highly transparent plate and a holographically-recorded optical element mounted on its surface; and a spectrum-splitting concentrator (SSC) that includes multiple, single junction PV cells that are separately optimized for high efficiency operation in respectively-corresponding distinct spectral bands. A conventionally-used HPC is deficient in that the collection angle, within which the incident solar light is diffracted to illuminate the solar cell, is limited to about 45 degrees. Production of a typical SSC, on the other hand, requires the use of complex fabrication techniques.
Volume holographic diffraction gratings have shown to be viable products for solar concentration. The gratings take the incoming light and bend the light to specific angles, based on the specific wavelength of light. With the appropriate grating and module configuration, the light that hits the grating is bent towards the PV material, increasing the amount of light it would see otherwise.
However, the production of volume holograms, especially those in the transmission configuration, is a time consuming process with low repeatability. Specifically, holograms are typically copied by positioning holographic recording film adjacent to a master holographic plate. The master hologram is then illuminated with a coherent reference beam, resulting in a replication of the curvature, direction, and wavelength of the original reference beam used to create the master hologram, which in turn creates a replica of the master hologram on the recording film. During this process, it is critical that the film and master holographic plate are fixed in place as any relative movement will corrupt the reproduction. Due to this limitation, current techniques require that significant time be expended stabilizing the system, which limits the rate at which the holograms can be replicated. Because the laser used to illuminate the master hologram is running the entire time and because it has a limited number of hours of continuous operation before it needs to be replaced or reworked, the stabilization time limits the amount of holographic film a laser can produce in its lifetime. Therefore a method and system is needed which allows for volume holograms, which are suitable for solar applications, to be mass produced in a cost-effective manner and which maximizes the productivity of the laser.